2008 YZ450F Head Problem

Hey guys,


I have a 2008 YZ450F. Bike wasn't running properly after firing it up after sitting for the winter. I did all the minor stuff like checking oils before starting it. Decided to check the valves and the clearance on the intake was out by .10mm  on each one. So I took the cams off and metal filings were sitting on top of the shim covers. The head looks destroyed and its scared so bad I cant even remove the shim covers unless I file away some of the overlapping aluminum lol. This is not good.


I am going to have to buy a new head and cams but was wondering if anyone has an idea what caused this so it don't happen again with the new parts. you can see in the pics what happened. Thanks






The head is repairable by a shop such as Engine Dynamics or Fastheads.  Looks like about $300.


This is caused by old, dirty oil that should have been changed, a general failure of the oiling system (Least likely of the 3), or improperly torquing down the cam caps.

Thanks for the response. At the end of last season I did put a new timing chain on it and the chain seemed pretty tight. Is it possible that a tight chain can do this?  I not only had to turn the tensioner all the way in, I also had to back the tension itself off the motor a little just to get the chain over the cams.


I was thinking it was an oil failure myself though, considering I couldn't get oil to come out of the oil pressure screw for the past 2 years. (I have another thread on here about that and we couldn't find the problem) There was oil on the cams though

You are supposed to REMOVE the tensioner when replacing the chain.  Ordinarily, the chain cannot be rolled over the second cam with the cam in place.  It needs to be assembled onto the sprocket in the position shown, then rolled back and down into position.



Good to know.. Thanks.. I am in the process of ripping the motor apart again. Found antifreeze in the oil. Gaskets look good so maybe an internal water pump seal gone? Oh man the troubles with this bike. Need to figure out why the oil is not coming from the oil pressure screw as well so a complete tear down it is.

 Found antifreeze in the oil. Gaskets look good so maybe an internal water pump seal gone?


Water pump can't contaminate the oil.  There's an air gap between the coolant and oil seals that leads to the outside just so that neither fluid can ever leak into the other one.  Your coolant is 90% likely to be from the head gasket.  Other than a crack in the head or cylinder, the only other points coolant can enter are at the O-ring where the right crankcase cover bolts up and at the base gasket.

Superhero Gray,


My friend has an 06 yz450f, and lost the tranny. He took it all apart and replaced the transmission with one from an 08 yz450f (it came out of my bike). We also switched his left side crankcase with mine because there was a lot of play in his shifting forks where it went into the case. After getting it all back together it fired up first kick.. Let it idle for a couple min. Shifted in first and it stalled. Started again and this time when going he shifted in third and bike stalled and locked up tire. couldn't get it to start again. Took it apart and intake cam jumped 90 degrees off timing. We did install a new chain and tensioner and followed the picture you put on for setting timing. Fixed timing, started bike and ran for 15 sec in neutral but then it shut off. Started taking it apart again and noticed a very similar problem that I just had.. See pic below.




It started to make a groove in the head below the cams. (Bike only ran for 2-3 min after rebuild and was not there before rebuilding)


Is there anyway my left side crank case could cause this? Or what's your thoughts?  We used a torque wrench when tightening his cam covers on...

Edited by yamie

Looks like lack of oil or lack of clearance.  The groove itself is something caused by some foreign material in the oil passage.  Either way, the head looks like it needs to go out to get the cam bores cleaned up.  Before the head comes off, you might want to get hold of a plastic bottle with a conical "squirt" cap and run some oil down from the head and see if the oilways are clear.  It should come out at the oil filter cover. 


One thing besides a damaged oil pump that can cause a drop in pressure is a worn crankshaft oil seal in the right crankcase cover.  Another is if the lower oil filter cover bolt hole was Heli-Coiled with too short an insert.  If that's the case, you can fix it this way:




Also, be sure that the piston cooling nozzle is in place. 



Overtightened the can tower bolts

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